This Research Scientist Award application continues a line of research aimed at learning how disturbance of the parent-infant relationship affects the developing young and may predispose to disorders of behavior and to stress-induced bodily disease. The animal model system we have developed in rats has led to the discovery of unexpected processes at work within the mother-infant interaction. We are learning how these regulatory processes mediate the effects of separation and shape the subsequent development of physiologic and behavioral systems of the infant. The disciplines involved are those of experimental psychology. biology and psychophysiology in particular, as adapted to immature experimental animals. The methods include selected electrophysiological, and microsurgical techniques as well as behavioral observation and recording. The aims are to understand the specific processes or mechanisms by which the experience becomes translated into altered physiological and behavior development. In the first of the three major sections of this proposal, basic processes involved in the immediate and the slower developing effects of maternal separation in 2 week old rats are analyzed, building upon our previous work in this area. In the second section we propose studies that will apply some of our recent knowledge about these basic processes to explore how they affect development of the infants' cardiovascular system, and influence the course of a new experimental model disease of respiratory regulation that we have recently described. In the third section, we will examine how a 24 hour separation affects the mother-infant interaction on reunion and thereafter. In the studies on the immediate response to separation, We will focus on the control of ultrasonic vocalization rates; in the other studies we will focus on 3 interrelated systems: autonomic control, nutrient intake, and sleep/wake state regulation.